Method of grinding helical forms



April 25, 1961 E. V. FLANDERS METHOD OF GRINDING HELIC'AL FORMS Filed March 17, 1959 2 Sheets-Sheet 1 INVENTOR Ernest [[Flazzders L AML $122M, MAL fin;

ATTORNEYS p 1961 E. v. FLANDERS 2,981,038

METHOD OF GRINDING HELICAL FORMS INVENTOR Erna??? V'Flamiens BY 5 V i ugmw, A oiwm J /%M, ,EZM ATTORNEY-5' METHOD OF GRINDING HELICAL FORMS Ernest V. Flanders, Springfield, Vt., assignor to Jones and Larnson Machine Company, a corporation of Vermont Filed Mar. 17, 1959, Ser. No. 799,936

6Claims, (Cl. 51-488) wheel, having the desired helical form dressed into the periphery thereof, radially into the Work piece to generate all the threads, up to the width of the wheel, simulta neously and without any relative axial movement between the work piece and the grinding wheel.

The prior known methods of thread grinding are of several types. In one known method a single ribbed wheel is set at the helix angle of the thread to be produced and the grinding is accomplished, often to full depth in a single pass of the wheel. The work is rotated by any conventional means and a feeding motion is produced to move the work axially a given amount during each revolution. In this method of grinding, the grinding wheel runs at a high speed which is unrelated to the angular velocity and axial feed of the work piece.

Another known method of grinding threads utilizes a plurality of annular grooves dressed in the periphery of the grinding wheel. In this method the work also rotates and traverses axially and the multi-ribbed wheel must go into the full depth of the threads very quickly. With this method only a few turns of the work completes the thread and the wheel is usually about as wide as the length of thread to be ground.

Thus, in the known prior art threads are generated by rotating the work and moving the work axially relative to the grinding wheel. This axial movement is positively geared to generate the proper pitch during the traverse. With the known methods of grinding all the cuts are of necessity fairly heavy, 'In grinding taps, for example, this results in a springing of the tap and the formation of a low cutting edge.

It is an object of this invention to provide a method of grinding helical forms which combines all the advantages of the known prior art without the disadvantages and allows helical forms to be ground by a simple plunge cut. For single ribbedwheel grinding, there must be many time-consuming traverses, and for multi-ribbed annular grooved wheel grinding the wheel must go to the full depth of the cut quickly or the work will move axially out from under the wheel with the same net result as using the single ribbed grinding wheel. With the method of this invention the grinding wheel and work do not move axially; thus a helical form up to the width of the wheel may be ground by moving the wheel radially with respect to the work.

Other objects and advantages of this invention will b pointed outinthe following descriptions and claims and illustrated in the accompanying drawings, which disclose, by way of example, the principles of this invention and the best mode which has been contemplated of applying these principles.

In the drawings:

Fig. 1 is a schematic side elevation view showing the States Patent grinding wheel and the work and illustrating the inventive concept of the disclosed method;

Fig. 2. is a schematic illustration of an apparatus'for practicing the method of this invention.

Generally, the inventive concept resides in grinding a helical form on a work piece with a grinding wheel having the same helical form dressed into the periphery thereof by setting the plane of the grinding wheel at the helix angle of the form to be ground on the work piece, rotating the work piece and the wheel at the same angular velocity, and moving the work piece and the wheel relative to each other in a direction radially of the work piece to accomplish plunge grinding of all the threads on the work piece up to the width of the wheel at the same time. By moving the wheel only radially, all the threads will be cut into the work piece at once and plunge grinding may be accomplished with a relatively heavy feed at first and a fade out at the end to accomplish final finish cutting with little pressure on the work. With a grinding wheel substani tially larger than the diameter of the work, the peripheral velocity of the Wheel will naturally be much greater than the peripheral velocity of the work, and the actual helix angle on the wheel itself will be very small. Thus, for practical purposes when the plane of the wheel is set at the helix angle of the work, the interference effect of a few minutes of helix angle in the wheel may be effectively ignored.

Referring to the drawings wherein the relative sizes and dimensions have been exaggerated for the sake of explanations, a work piece 10 may be supported and positively driven by driver support 12 and dead support 14. It is desired to generate a helical form 16 on this work piece by means of the method disclosed herein.

A grinding wheel 20 is suitably dressed to provide a helical form 22 on the periphery thereof. The pitch of the helical form 22 on the wheel 20 and the pitch of the helical form 16 on the work piece 10 are identical. The plane of the wheel 20, i.e., a plane normal to the rotative axis, is preferably set at the helix angle 5 of the thread 16 on the work piece 10. The wheel 20 having the helix 22 formed in the periphery thereof will actually cause a small interference, but this is a negligible quantity because the helix angle of the helix on the wheel is very small due to the large diameter of the wheel.

The setting of the plane of the wheel 20 to the helix angle of the helical form 16 on work piece 10 may be accomplished by any suitable means, not shown. This setting may be adjustable to accommodate diiferent work pieces and different helix angles.

As shown in Fig. 2, means are provided to'drive the wheel and the work at the same angular velocity. The work 10 is driven by axial support 12' powered by a work drive motor 24, which may be an electric motor or the like. The wheel 20 is driven at the same angular velocity as the work 10 by another suitable electric motor 26. The motors 24 and 26 may have a timing chain 28 trained around sprockets 30 and 32 attached to the rotors thereof to assure that the motors are driven in synchronism and that the rotation of the work 10 and wheel 20 will always be at the same angular velocity. A suitable source of electricity may be applied through electrical connections 34 to motors'24 and 26 simultaneously. Although an electric motor drive with mechanical synchronization means is shown, any other suitable drive means for driving the work and the wheel at the same angular velocity could be used.

Any suitable means, not shown, can be utilized to feed the wheel 20 and work 10 relative to each other in a radial direction with respect to the work piece. There will be no relative axial motion between the wheel and the work piece.

Of course, when the helix 22 dressed in the periphery of the wheel 20 wears down and loses its form, it is necessary to redress this wheel. This redressing or truing is accomplished by a suitable diamond point tool 34 mounted on a support 36 for travel along a screw 38 in slideway 40. A truing motor 42 is adapted to drive the diamond tool at a suitable ratio through a gear train having gears 44, 45, 46 and 47. A clutch 48 is provided for connecting r disconnecting the drive of the truing motor 42 to sprocket 52. A suitable sprocket 50 is on the axis of the wheel 20 and sprockets 50 and 52 are connected by a timer chain 54 such that the rotation of the wheel 20 may also be synchronized with the traverse of the dressing tool 34. The single point diamond dressing tool 34 may be traversed across the face of the grinding wheel by the above-described mechanism to produce the proper pitch upon the grinding wheel periphery. This dressing may be done slowly to avoid the need of fast diamond action. However, since the work pieces are ground with all the ribs of the helix 22 working at once, many pieces will be ground between the dressing of the wheel.

The wheel 20 and the work 10 may be rotated in the same direction, in which case the peripheral velocities will add, or they may be run in the opposite direction, in which case the peripheral velocities would subtract. This choice of direction of rotation could be made to accommodate the best grinding condition. However, once the choice of direction of rotation is made, it will dictate whether the wheel 20 carries a right or left hand thread, but, of course, either could be provided by the truing mechanism.

In operation, with the work 10 and the wheel 29 rotating at the same angular velocity, the wheel 20 having the helix 22 dressed therein, which helix has the same pitch as helix 16, will then be rotating in a much greater peripheral velocity than the work 10 due to the larger diameter of the wheel. For best results, the plane of the wheel 22 is set at an angle equal to the helix angle on the work and the helix angle 0 of the thread on the wheel relative to the plane of the wheel will be negligible due to its much larger diameter. Then the wheel or the work are moved radially with respect to the work by any conventional type of feeding arrangement to accomplish plunge grinding of the work. This radial feed may be heavy at first, to remove the bulk of the stock, and then may fade to a sparkout. Thus, at the finish of the grinding, the stresses in the machine and the deflection of the work are at a minimum and the final size may be achieved with great accuracy.

As a specific example illustrating the principles set out above, a .250 inch diameter work piece may have a 20 pitch thread thereon. Thus, the helix angle 1) of the threads on the work piece will be 338. With a 20 inch diameter grinding Wheel utilized to grind the thread or helix on the work piece. the helix angle 0 on the grinding wheel will be less than 3 minutes and hence will be negligible, even when the plane of the wheel is set at the helix angle s of the thread on the work piece.

While there have been shown and described and pointed out the fundamental novel features of this invention as applied to a preferred embodiment. it will be understood that various omissions and substitutions and changes in the form and details of the disclosed method may be made by those skilled in the art without departing from the spirit of the invention. it is the intention, therefore, to be limited only as indicated by the scope of the following claims and reasonable equivalents thereof.

What is claimed is:

1. A method for grinding a helical form in a work piece comprising: contacting the work piece with a grinding wheel, the plane of the wheel being set at the helix angle of the desired helical form to be ground in the work piece, said grinding wheel having a helical form dressed into the surface thereof, the helical form in the periphery of the wheel having the same pitch as the helical form to be ground on the work piece, the diameter of the wheel being sufiiciently large with respect to the diameter of the work piece that the helix angle of the helical form on the periphery of the wheel is negligible, rotating the work piece and the wheel at the same angular velocity, and moving said work piece and wheel relative to each other only in a direction substantially radially of the work piece to simultaneously grind the threads of the work piece by the wheel.

2. A method for grinding a helical form in a work piece with a substantially larger grinding wheel having the same helical form dressed into the peripheral surface thereof, comprising, setting the plane of the grinding wheel substantially at the helix angle of the helical form to be formed on the work piece rotating said work piece and said wheel at the same angular velocity, and moving said work piece and said wheel relative to each other only substantially radially of said work piece while in contact and cutting engagement to accomplish the formation of all threads in the work piece at the same time.

3. A method of grinding a helical form in a work piece with a grinding wheel of substantially larger diameter than the work piece having a helical form dressed into the periphery thereof, the helical form in the periphery of the wheel having the same pitch as the helical form to be ground on the work piece, the method comprising: setting the plane of the wheel substantially at the helix angle of the work, rotating the work piece and the wheel at the same angular velocity, whereby due to the difference in diameter the grinding wheel will have a substantially greater peripheral velocity, and moving said work piece and said wheel relative to each other and in contact with each other only in a direction substantially radially of the work piece to generate a helical form in the Work piece having a pitch identical with the helical form dressed in the wheel.

4. A method of grinding a helical form in a work piece comprising: providing a grinding wheel with a periphery having a helix therein with a pitch equal to the pitch of the helical form to be generated in the work piece, contacting the work piece with the grinding wheel of substantially larger diameter than the work piece, with the plane of the wheel set substantially at the desired helix angle of the helical form to be ground in the work piece, rotating the Wheel and the work piece at the same angular velocity, whereby due to the difference in diameters the grinding wheel will travel at a substantially greater peripheral velocity, and feeding the work piece and Wheel relative to each other only in a direction radially of the work piece to generate a helical form in the work piece having a pitch equal to the pitch of the helical periphery of the Wheel and a length equal to the Width of the Wheel.

5. A method of grinding a helical form in a work piece by a grinding wheel with a diameter substantially larger than the work piece and having the same effective axial length as the helical form to be ground, the wheel also having its periphery provided with a helical form which has the same pitch as the helical form to be ground in the work piece, the method comprising: setting the plane of the grinding wheel at an angle equal to the helix angle of the helical form on the work piece, rotating the work piece and the wheel at the same angular velocity, and feeding the work piece and wheel relative to each other while in contact with each other only substantially radially of the work piece to grind all the threads on the work piece up to the effective axial length of the wheel simultaneously.

6. A method as defined in claim 5 further comprising: dressing the desired helical form in the periphery of the wheel.

References Cited in the file of this patent UNITED STATES PATENTS 1,496,083 Browne June 3, 1924 2,690,089 Bedker Sept. 28, 1954 2,792,824 Rickenmann May 21, 1957 

